Genes for color blindness and hemophilia are linked on the X-chromosome in humans with a recombination frequency of 30%. A woman whose father was a color blind hemophiliac and mother was normal with no history of color blindness and hemophilia wants to have children. The prospective father is normal with no history of either colorblindness or hemophilia in his family. what is the probability that she will have a normal child?

1.) 0.702.) 0.6753.) 0.504.) 0.355.) 0.306.) 0.15

Any help would be appreciated. I have tried so hard to figure out how to answer this, and I just cannot figure it out.

Since man has only one X chromosome, she must have one X defective and one X normal (from mother). In 30% of cell divisions the chromosomes recombine and form two defective X chromosomes (each for other disease, but they ask for normal kid, so any of these chromosomes will be ruled out). In the other 70% cases the chromosome will be defective in 50% and normal in 50%, i.e. 35% of total cases. Thus 4.) is the right answer.